Variation in A Species List the features which differ within these dog breeds.

Types of Variation Some variation is CONTINUOUS. This means that it may have any one of a large range of values. E.g. height. This means that it may have any one of a large range of values. E.g. height. Some variation is DISCONTINUOUS. This means that it can only have one of a fixed number of options. E.g. eye colour

Continuous and Discontinuous Variation Fill in the table to indicate whether the variation is continuous or discontinuous. Fill in the table to indicate whether the variation is continuous or discontinuous. FeatureVariation Eye colour Weight Shoe size Height Skin colour Tongue rolling

Selective Breeding If an animal has a feature which is particularly useful, then farmers or breeders may allow that animal to breed in order to pass the useful feature onto the next generation. If an animal has a feature which is particularly useful, then farmers or breeders may allow that animal to breed in order to pass the useful feature onto the next generation.

Selective Breeding In Sheep. On your own. List 5 features that might be important to breed into sheep. With your partner. Compare your lists. Can you prioritise these features ? As a class Can we agree on the important features?

Selecting Characteristics. On your own. Look at the table of Information. Which pairs of sheep would you use to; 1.Breed sheep with good wool and good meat? 2. Breed sheep with good wool that can survive harsh winters? winters? BreedFeatures Balwen Lives in cold, harsh conditions Blue-faced Leicester Good quality wool Polled Dorset Good quality meat Fresian Makes a lot of milk

What About Plants ? Complete the following passage. In plants two types of reproduction can take place. Sexual – where the male ______ has to fertilise the female ______ to make a seed. This makes plants that have ________features to the parents. Asexual- where a new plant is grown from a root or stem cutting of one parent. This produces _________offspring to the parent. Identical pollen different ovule

Commercial Plant Growers In large garden centres in the summer there are large numbers of identical palnts. In large garden centres in the summer there are large numbers of identical palnts. 1.How have these plants been produced? 2. What advantages are there to the grower in doing this? 3 What disadvantages are there to doing this?

Extension Material. Some selective breeding is done for fashion reasons. Consider the following slides carefully

Is it all good news?  Sometimes breeding between close relatives makes genetic deformities more frequent.  British Bulldogs for example have such large heads that they are unable to be born without Caesarean Section. They are prone to breathing difficulties and heart problems.

The Future?  Cat breeders in Texas have deliberately crossed two cats with front paw deformities to produce a breed with tiny front paws.  They have called this the Twisty Cat or Kangaroo cat.  What do you think?

Homework. What are your views on ; A. Farmers using selective breeding to produce more valuable livestock more suited to today’s foodmarket. B. Breeders mating closely related pedigree animals despite the risks of deformities C. Breeders producing new strains of animal which differ greatly from the natural varient.